Cooling of hot bodies

ABSTRACT

An apparatus for cooling a vessel containing molten metal has a quantity of liquid coolant atomized by a gaseous medium and onto a surface to be cooled. The supply of gaseous medium is constant while the supply of liquid coolant to the spray nozzles is controlled by at least one valve the operation of which is brought about by a non-electrical temperature responsive element in thermal contact with the surface to be cooled. The rate at which the liquid coolant is sprayed on to the hot surface is controlled such that the volume of coolant sprayed on to the surface to be cooled does not exceed the volume of liquid that is capable of being vaporized from the surface.

This invention relates to a method of cooling a hot body and to a bodywhich, in use, has to be cooled with liquid coolant. A particular, butnot sole, application of the invention is to a method of cooling a partof a vessel containing molten metal and to such vessels.

In pyrometallurgical processes, heat is generated during the smelting,melting or refining of the metal. The process ingredients are usuallyrefined within a steel vessel which is lined with refractory material inorder to protect the steel shell, as far as possible, from the hightemperatures used in the process. Nevertheless, the shell usuallybecomes hot so it is beneficial to provide cooling of at least part ofthe shell in order that distortion is reduced and the shell materialretains sufficient of its strength to operate according to theDesigner's intentions.

It is now well recognised in the metallurgical industry that it isextremely dangerous to allow liquid water and liquid metal to come intoclose proximity to one another because, in the event of a faultoccurring, the sudden expansion and vaporisation of water in contactwith liquid metal can cause a dangerous explosion.

It is known from WO 89/03011 to cool a hot metal body forming part of avessel containing molten metal by applying droplets of liquid coolant tothe outer surface of the body in a controlled manner such that thevolume of coolant applied in a given time period does not exceed thevolume of coolant which is vaporised by contact with the hot surface inthe given time period. In this document, it is disclosed that, in orderto control the amount of liquid coolant applied to the outer surface ofthe body, one or more thermocouples are used to determine thetemperature of the surface and this information is transmitted to atemperature controller remote from the body. This controller controlsthe supply of liquid coolant passing through one or more valves, alsoaway from the body, to one or more sprays located adjacent to the body.

It is also known from EP-0044512-A to cool a vessel with a cooling boxfitted into the wall of the vessel and the box contains a heat exchangesurface onto which a cooling liquid is sprayed. The quantity of liquidsprayed onto the surface is controlled by a temperature measuring deviceso that a spontaneous evaporation of the cooling liquid occurs.

It will be appreciated from this description of the prior art that theprovision of thermocouples on the surface to be cooled and one or morevalves and a controller remote from the surface inevitably means thatthere are long electrical connections and coolant lines between thesurface and the remote position where the valves and the controller arelocated.

An object of the present invention is to provide an improved method ofcontrolling the surface temperature. The result is usually a reductionin capital cost and more sensitive control of surface temperature.

According to a first aspect of the present invention, in a method ofcooling a hot body, a quantity of liquid coolant is sprayed onto asurface of the body to be cooled by one or more spray nozzles, and thevolume of liquid coolant applied in a given time period is controlled sothat it does not exceed the volume of liquid coolant which is vaporisedby contact with the surface of the hot body in the given time periodcharacterised in that a gaseous medium is supplied continuously to theor each spray nozzle and the liquid coolant which is atomised by thegaseous medium into droplets is supplied to the or each spray nozzleunder the control of at least one valve the operation of which isbrought about by the action of a non-electrical temperature responsiveelement in thermal contact with the surface.

It will be appreciated that, since the or each valve which controls thesupply of liquid coolant to the or each spray nozzle is in turncontrolled by a non-electrical temperature responsive element which isin thermal contact with the surface to be cooled, it will be clear thatthe valve is on, or very close to, the surface to be cooled and theelement may be considered to be part of the valve. There are noelectrical connections between sensors on the surface and either thevalve or a controller at a position remote from the surface. The controlof liquid coolant is determined entirely by the or each valve which ison, or very close to, the surface. The part of the element which is inthermal contact with the surface is conveniently a chamber embedded inthe surface and which is connected to the valve by a capillary tubecontaining a fluid. An increase in temperature to the controltemperature causes thermal expansion or an increase of the vapourpressure of the fluid in the element/capillary tube and opens the valve.

According to a second aspect of the present invention, a body, which inuse has to be cooled with liquid coolant, said body having one or morespray nozzles arranged to receive liquid coolant and gaseous medium andto discharge droplets of atomised coolant onto a surface of the body, atleast one valve which serves to control the supply of liquid coolant tothe or each nozzle and which is operated under the action of anon-electrical temperature responsive element in thermal contact withthe surface of the body so that the volume of coolant applied in a giventime period does not exceed the volume of liquid coolant which isvaporised by contact with the surface of the hot body in the given timeperiod.

A single valve may control the supply of liquid coolant to a singlenozzle, to a single spray bar upon which two or more nozzles may bemounted, or to a group of spray bars. Conveniently, each valve ismounted on a branch pipe connected to a ring main through which thecoolant circulates. The pressure within the ring main is controlledwithin limits so that, if any valve on the vessel is open to supplycoolant to the or each spray nozzle to cool the relevant part of thevessel, make-up coolant is supplied in a controlled manner to the ringmain.

In use, the temperature of the surface to be cooled is sensed by theelements. As the surface temperature rises, eventually the valve opensand allows coolant to flow to the or each spray nozzle. Air iscontinuously supplied to the or each nozzle so, as soon as liquid issupplied to the nozzle, atomisation of the coolant is achieved at lowpressure and efficient evaporative cooling results in the region wherethe atomised coolant is deposited. As a result of the droplets ofatomised coolant being deposited on the surface, the surface and elementin contact with the surface cool and eventually the valve is closed. Thesystem may be tuned to operate over a required temperature range,typically between 300° C. and 250° C. though, with advantage, between,for example, 250° C. and 200° C. when small surface areas may be treatedindependently.

In many applications, the vessel temperature is far from uniform. Forexample, in steel making, a vessel containing molten metal may be tiltedless to a charging side than to a tapping side. This results in a buildup of slag on the charging side while the vessel lining on the tappingside wears away. Consequently, the vessel shell on the tapping sidetends to be hotter than on the charging side. In order to satisfy thesediverse cooling requirements, each region of the vessel requires its owncooling system under its own independent control.

The present invention provides an arrangement by which a simple controlsystem may be used, for example, for the whole of the top cone region ofthe vessel while allowing for different cooling requirements around thecircumference of the vessel.

It is convenient for the gaseous medium, conveniently air, to becontinuously supplied to the spray nozzles so that, when no cooling isrequired, dust is excluded from the nozzles. It is also convenient forthe thermostatic valves to be constructed so that when no cooling isrequired, the valves and the spray nozzles are purged of coolant,usually water, and this reduces the possibility of evaporation ofcoolant in the spray bars and nozzles which would result in thedeposition of dissolved solids inside them.

In order that the invention may be more readily understood it will nowbe described, by way of example only, with reference to the accompanyingdrawings in which FIGS. 1 and 2 are diagrammatic perspective views of apart of a steel making vessel illustrating alternative embodiments ofthe invention.

The cone defining the open top of a furnace vessel is indicated byreference numeral 1. Extending around the outer surface of the cone is amain pipe 2 having connections (not shown) by which air under pressureis supplied to the pipe. Similarly, a main pipe 3 extends around thecone and connections (not shown) supply coolant liquid, usually water,to the pipe.

The outer surface of the cone is divided into regions 4 by spraystructures 5 which are located in spaced apart relation around thesurface of the cone. Each structure comprises an air pipe 6 and a waterpipe 7. The air pipe is connected at one end to the air main pipe 2 andis closed at the other end. The water pipe 7 is connected at one end toa valve 8 and the other end is closed. The valve is connected to themain pipe 3. A plurality of air-mist nozzles 9 are connected to thepipes 6 and 7. The surface of each region 4 has a non-electricaltemperature responsive element in thermal contact therewith. In thearrangement shown in FIG. 1 each element 10 comprises a bulb in a pocketformed in the surface and the bulb is connected to the valve 8 by acapillary tube 11. A fluid is present in the bulb and the capillarytube. The valve 8 is operable by changes in pressure applied to it bythe fluid in the bulb and capillary tube.

In the FIG. 1 arrangement, in use, air under pressure is supplied to thepipe 2 and by way of the pipes 6 to the nozzles 9. Water is suppliedunder pressure to the pipe 3 and hence to the valves 8. The valves arenormally closed so that the water is not supplied to the nozzles 9. Thesurface temperature of each region 4 is transmitted from the sensor partof the element in contact with the surface to the valve and at theappropriate temperature the expansion or pressure of the fluid in thecapillary tube 11 opens the valve 8 to allow water to flow to the pipe 7and hence to the nozzles 9 where a fine mist is directed over the region4 of the surface. As the surface and sensor cool, the expansion orpressure of the fluid in the sensor/capillary tube falls and eventuallythe valve closes cutting off the water supply to the correspondingnozzles.

In the alternative arrangement shown in FIG. 2, the temperatureresponsive element 12 is an open/shut valve which is thermostaticallycontrolled. Air from the main pipe 2 is supplied to the input of theelement 12 by a small bore tube 13 and the outlet of the element isconnected to the valve 8 by another small bore tube 14. The element 12may be operated by bi-metallic expansion or by expansion of a fluidcontained in a chamber in the element. As the surface reaches the designtemperature, element 12 opens, allowing air to pass through the tubes 13and 14 to operate the valve 8. Similarly when the temperature drops, theelement 12 closes and tube 14 is vented to atmosphere allowing valve 8to close. Alternatively, the element 12 may open and close at the upperdesign temperature. As the temperature increases through say 300° C. theelement 12 opens. This allows valve 8 to operate. As the temperaturefalls through 300° C. element 12 closes and isolates the air volume intube 14 keeping the valve 8 open. At the lower design temperature, say200° C., a small vent within the element 12 opens, releasing thepressure of the air in the tube 14 thereby allowing the valve 8 toclose.

It will be appreciated that by supplying the appropriate number of spraystructures 5 each controlling a separate region, the size of each regioncan be reduced to produce an accurate control of the temperature of theregion. Furthermore, some regions may be deliberately arranged tooperate at different temperatures.

We claim:
 1. A method of cooling a hot metal body which forms part of avessel containing molten metal, comprising the steps of disposing aplurality of spray nozzles in relation to a surface of the body to becooled; arranging a non-electrical temperature responsive element inthermal contact with the surface of the body to be cooled; supplyinggaseous medium continuously to the nozzles; supplying liquid coolant tothe nozzles under the control of at least one valve operated by theaction of said temperature responsive element for the liquid coolant tobe atomised into droplets by the gaseous medium and the droplets to besprayed onto the surface of the body and said valve being controlledsuch that the volume of liquid coolant applied to the surface in a giventime period does not exceed the volume of liquid coolant which isvaporised by contact with the surface of the hot metal body in the giventime period.
 2. A method as claimed in claim 1 in which the surface ofthe body to be cooled is considered to be divided into regions each ofwhich receives liquid coolant from one or more spray nozzles, and theliquid coolant is supplied to said one or more spray nozzles under thecontrol of at least one valve the operation of which is brought about bythe action of a non-electrical temperature responsive element in thermalcontact with said region of the surface.
 3. A method as claimed in claim1 in which at least one temperature responsive element includes a fluidand the operation of its associated valve is brought about by changes inthe vapour pressure of the fluid.
 4. A method as claimed in claim 1 inwhich at least one valve is operated in response to the supply of agaseous medium thereto, said supply of said gaseous medium beingcontrolled by said temperature responsive element.
 5. A metal body whichis to be cooled and which forms part of a vessel containing moltenmetal, a plurality of spray nozzles disposed in relation to a surface ofthe body to be cooled; a non-electrical temperature responsive elementarranged in thermal contact with the surface of the body to be cooled; agaseous medium connected to be supplied continuously to the nozzles;means for supplying liquid coolant to the nozzles under the control ofat least one valve operated by the action of said temperature responsiveelement for the liquid coolant to be atomised into droplets by thegaseous medium and the droplets to be sprayed onto the surface of thebody and means for controlling said valve such that the volume of liquidcoolant applied to the surface in a given time period does not exceedthe volume of liquid coolant which is vaporised by contact with thesurface of the metal body in the given time period.
 6. A vessel asclaimed in claim 5 in which there are a plurality of said spray nozzlesarranged adjacent said surface so that the surface can be considered tobe divided into regions each of which receives the droplets from one ormore spray nozzles and the supply of liquid coolant to the or each spraynozzle supplying droplets to each region is controlled by a separatevalve and a separate non-electrical temperature responsive element inthermal control with said region of the surface brings about theoperation of said valve.
 7. A body as claimed in claim 5 in which the atleast one temperature responsive element is connected to its valve by acapillary tube containing a fluid and arranged such that operation ofthe valve is brought about by changes in the vapour pressure of thefluid.
 8. A body as claimed in claim 5 in which the at least one or eachelement includes a bi-metal the operation of which controls the flow ofan actuating gas to the valve with which it is associated.
 9. A vesselas claimed in claim 5 in which the body is a cone defining the open topof a furnace vessel.